LONDON – In October last year, bulk carrier CS Caprice was shipping a cargo of barley across the Mediterranean when it answered a call to help about 500 people who were drifting north of Libya without a skipper. A brewing storm threatened to capsize their tiny fishing boat.

“They had no food or water and they had been three days at sea, ” said the ship’s captain, Joshua Bhatt. “When they showed small infants to us, it was a really pathetic sight … They were asking, ‘can you take us to Italy?’”

Like any merchant ship, the crew of the Caprice was bound by the United Nations Convention on the Law of the Sea, to “render assistance to any person found at sea in danger of being lost.” Such rescues used to be rare. But as the number of refugees and migrants attempting to get to Europe has spiked over the past two years, it has drawn in more and more vessels like the Caprice.

Since January 2014, more than 1, 000 merchant ships have helped rescue more than 65, 000 people, according to estimates from the International Chamber of Shipping. That’s more than one in 10 of the estimated 585, 000 migrants and refugees who crossed the Mediterranean over the period. Commercial shipping companies have been “absolutely heroic, ” said Melissa Fleming, chief spokeswoman for the United Nations refugee agency.

But shipping companies are increasingly frustrated with that role. They are prepared to help, they say. But they want governments to take more of the burden.

One problem is cost. Insurance covers some expenses when a ship is forced to conduct a rescue – but not the loss of business, which ranges from $10, 000 per day for cargo ships to more than $50, 000 for oil tankers. A more important concern is security.

“Merchant ships are being used as radio taxis to pick up people, ” said Harry Hajimichael, general manager with Greek-based operator Tsakos Shipping and Trading, four of whose vessels were involved in rescuing more than 600 people in the Mediterranean last year. “This is not the right way to do it.”

For firms like the Bahamas-based Campbell Shipping, which manages the Caprice, the main worry is who they might be rescuing. “We do not know who we are taking onboard: There are no papers, there are no background checks, ” said Rajesh Dhadwal, senior manager for marine and safety at the company. “What if among the people rescued, a few are part of Islamic State or a terrorist organisation, and they … take over a tanker?”

The European Union (EU) says it has responded to the concern, tripling the budget of border management agency Frontex. “We have now deployed at sea the largest operation in the history of Frontex and of the operational cooperation among the Member States at the external borders, ” a spokeswoman said by email.